The modification of societies as a function of population movements yields profound transformations of the economical and socio-political contexts of numerous countries. The question is whether these transformations lead to particular changes into educational systems, into knowledge transmission, with respect to knowledge content and to knowledge learning processes. How to manage knowledge diversity and common knowledge, socialisation diversity and common culture ? New propositions emerge that aim at transforming the implicit and often «monocentric» perspective of the school contract; These suggestions enhance approaches based on plurality, on individual and collective resources considered as components of the social process of learning and knowledge acquisition. We will discuss the illusion of homogeneous educational systems, by briefly analyzing the steps schools (and perhaps even more research) of immigration countries have gone through over the last 40 years.